Nanofibres are an interesting phase into which amphiphilic molecules can self-assemble. Described for a large number of synthetic lipids, they were seldom reported for natural lipids like microbial amphiphiles, known as biosurfactants. In this work, we show that the palmitic acid congener of sophorolipids (SLC16:0), one of the most studied families of biosurfactants, spontaneously forms a self-assembled fibre network (SAFiN) at pH below 6 through a pH jump process. pH-resolved in situ small-angle X-ray scattering (SAXS) shows a continuous micelle-to-fibre transition, characterized by an enhanced core–shell contrast between pH 9 and pH 7 and micellar fusion into a flat membrane between pH 7 and pH 6, approximately. Below pH 6, homogeneous, infinitely long nanofibres form by peeling off the membranes. Eventually, the nanofibre network spontaneously forms a thixotropic hydrogel with fast recovery rates after applying an oscillatory strain amplitude out of the linear viscoelastic regime: after being submitted to strain amplitudes during 5 min, the hydrogel recovers about 80% and 100% of its initial elastic modulus after, respectively, 20 s and 10 min. Finally, the strength of the hydrogel depends on the medium's final pH, with an elastic modulus fivefold higher at pH 3 than at pH 6.

This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)’.

纳米纤维是一个有趣的相，两亲分子可以在其中自组装。被描述为大量合成脂质，它们很少被报道用于天然脂质，如微生物两亲物，称为生物表面活性剂。在这项工作中，我们表明槐糖脂的棕榈酸同系物 (SLC16:0) 是研究最多的生物表面活性剂家族之一，通过 pH 跳跃过程在 pH 低于 6 时自发形成自组装纤维网络 (SAFiN)。pH原位解析小角 X 射线散射 (SAXS) 显示出连续的胶束到纤维的转变，其特征在于 pH 9 和 pH 7 之间增强的核壳对比度以及胶束在 pH 7 和 pH 6 之间融合成平坦的膜。在 pH 值低于 6 时，通过剥离膜形成均匀的、无限长的纳米纤维。最终，纳米纤维网络在线性粘弹性状态之外施加振荡应变幅度后，自发形成具有快速恢复率的触变性水凝胶：在 5 分钟内经受应变幅度后，水凝胶恢复了其初始弹性的约 80% 和 100%分别在 20 秒和 10 分钟后的模量。最后，水凝胶的强度取决于介质的最终 pH 值，其弹性模量在 pH 3 时比在 pH 6 时高五倍。

本文是主题问题“用于新兴技术的生物衍生和仿生可持续先进材料（第 1 部分）”的一部分。